This invention relates to methods for reducing the power dissipation in power transistors of the MOS=Metal Oxide Semiconductor type. The invention is not applicable to transistors of non-insulated gate structure e.g. bipolar types.
The power transistor is used for the purpose of controlling the current in an external load. The transistor acts as a variable resistance, therefore the current flowing will inevitably cause a certain heat to be dissipated. This heat is detrimental to the junctions of transistors, causing a faster deterioration, finally leading to malfunction. In order to dissipate more power, the transistor has to be made physically larger, therefore more expensive.
Therefore, one attempts to reduce the power dissipation in power-transistor devices for example by using fastswitching circuits, but these are complicated and cause many disturbances. Alternatively the cooling has to be improved with heat-exchangers or the so called heat sinks and even with forced air cooling.
All of these disadvantages are overcome in a simple way by this invention. The principle--using a resistor to reduce the dissipation in the transistor, and "move" it to the resistor--is well known. But not until the invention of the MOS-transistor has the road been opened to carry out simple control and dividing arrangements for the transistor and resistor-current.